How did Earth get its atmosphere?
Photo: wildpianist
It’s thought that Earth had an atmosphere when it formed four-and-a-half billion years ago. But that early atmosphere probably consisted of hydrogen and helium, the two most common elements in a vast cloud in space – and the elements from which Earth is thought to have been born.
Our planet’s first atmosphere probably lasted only a few hundred million years. Earth was very hot at first, and light gases like hydrogen and helium would soon have escaped into space. A second atmosphere replaced the first one – in a process that’s still happening today.
Earth’s present atmosphere is thought to have come from inside the planet. Volcanos might have spewed out water vapor, nitrogen compounds, carbon dioxide, ammonia, and methane. Interactions with radiation from the sun – and falling temperatures – caused large amounts of nitrogen to appear. Eventually, life came on the scene to add breathable oxygen and protective ozone, creating the air we breathe today.
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